The present invention relates to an X-ray photographing apparatus of a power driving type which moves forwardly or backwardly in response to a force of an operation handle. More particularly, the present invention relates to a movable type X-ray photographing apparatus, which includes bridge circuits for driving formed of switching elements; driving motors, each being positioned at a center of the bridge circuit; and pulse width control circuits for controlling ON-OFF duty of torque of the motors by the bridge circuits.
FIGS. 2(a) through 2(c) show a movable type conventional X-ray photographing apparatus. FIG. 2(a) shows a front view of the movable type conventional X-ray photographing apparatus; FIG. 2(b) shows a side view; and FIG. 2(c) shows a plan view. This apparatus is formed of an X-ray tube 18; an arm 19 for supporting the X-ray tube 18; a column 20 which is rotatable on a truck or base 21; an ascending and descending section in which the arm 19 moves vertically or up and down along the column 20; and freely rotatable or pivotable front wheels 23 and rear wheels 22 (right wheel 2 and left wheel 1) which are incapable of steering. The truck 21 is provided with an X-ray control section, and moves forwardly or backwardly by means of driving motors (a right motor 6 and a left motor 5) provided at a lower section when a lever handle 14 disposed in a handle supporting base 17 attached to the truck 21 is operated forwardly or rearwardly.
The arm 19, which includes a supporting mechanism for the X-ray tube 18 and a rotational mechanism therefor and extends or retracts horizontally, moves smoothly vertically along the column 20, so as to be balanced. A collimator (X-ray radiation port) of the X-ray tube 18 is directed to any directions and spatial positions in accordance with a photographing portion of a subject, that is, a person to be examined.
Since the weight of the movable type X-ray photographing apparatus may become more than 450 kg, it is very difficult to move the truck or base without help of the power. In general, a rear portion of the truck 21 is provided with a pair of rear wheels 22, which are attached not to be steered, and a front portion of the truck 21 is supported by a pair of casters. That is, front wheels 23 are freely rotatable or can be turned. The rear wheels 22 are generally driven by the driving motors (the right motor 6 and the left motor 5) mounted in the truck.
The truck 21 includes an internal power supply formed of an automobile battery and an inverter with a main circuit of 100-120 V and 60 Hz, and the truck 21 also includes a high-voltage transformer and a condenser. In many cases, there is used an apparatus of a one-touch system, wherein a control circuit thereof is solid-systematized and a photographing operation is automatically programmed.
Also, rubber tires or the like are used in the truck 21, so that the apparatus can freely enter or leave a patient""s room, an operating room, or an elevator, and the truck 21 also includes a brake system, a cassette box, and accessories.
It is important that the movably type X-ray photographing apparatus is small, light-weight, and excellent in a moving operation ability as a mobile type apparatus. Also, the X-ray photographing apparatus is easily moved to a bedroom, a technician room, an operating room, a children room or a pediatric room, an X-ray room, an infant room or the like in a hospital, and conveniently used for an X-ray photographing or radiography at a job site, that is, the location where the apparatus is moved.
FIG. 3 shows a control block diagram of the movable type X-ray photographing apparatus. A left wheel 1 and a right wheel 2 shown in an upper section in FIG. 3 are respectively driven by the left motor 5 and the right motor 6, and the left motor 5 and the right motor 6 are individually controlled by a motor driving circuit 9 through a left output 7 and a right output 8. The motor driving circuit 9 is subjected to a switching control by pulse width modulation (PWM) by means of a PWM control circuit 10. A duty control width of the switching control is controlled by a signal from a CPU (central processing unit) 35. When an operator operates the lever handle 14 of the truck 21 forwardly or rearwardly, signals from a left pressure sensor 15 and a right pressure sensor 16 disposed at both ends of the lever handle 14 are individually inputted to the CPU 35 as a left input 12 (left Ft) and a right input 13 (right Ft).
On the other hand, from a left encoder 3 and a right encoder 4, which are respectively provided at axles of the left wheel 1 and the right wheel 2 and detect rotational speeds, signals of a rotational speed Vt at left and a rotational speed Vt at right are inputted to the CPU 35. Then, the CPU 35 controls the PWM control circuit 10 with PWM control width which is proportional to the input signals Ft of the forward or backward movement from the left pressure sensor 15 and the right pressure sensor 16. Accordingly, the motor driving circuit 9 is actuated, and the left motor 5 and the right motor 6 are rotated at output torque T. The rotational speeds Vt of the motors are detected by the left encoder 3 and right encoder 4, and the speed signals Vt are inputted to the CPU 35.
If the rotational speeds Vt are lower than a predetermined rotational frequency or number corresponding to the input signals Ft, the PWM control width is enlarged, and if the rotational speeds Vt are higher than the aforementioned predetermined rotational frequency or number, the PWM control width is narrowed. The rotational speeds are fed back and controlled. The CPU 35 inputs the duty control width signal corresponding to the PWM control width into the PWM control circuit 10; the PWM control circuit 10 controls the motor driving circuit 9; and the motor driving circuit 9 controls the rotational speeds V of the left motor 5 and the right motor 6.
The lever handle 14 is connected to the truck 21 through spring members which are relatively rigid but flexible. The spring members connected to both sides of the truck 21 are formed of hard plate springs, and by providing these spring members, the position of the lever handle 14 can be changed slightly in the front and rear directions in response to the force applied to the lever handle 14, such as a force for pushing or pulling the lever handle 14.
At both ends of the lever handle 14, a pair of linear magnets moving together with the lever handle 14 is respectively attached. On the other hand, a pair of Hall-effect sensors (the left pressure sensor 15 and the right pressure sensor 16) is attached to the truck 21, and disposed respectively adjacent to the corresponding magnets. The Hall-effect sensors are respectively connected to power supplies (not shown). When the Hall-effect sensor (left pressure sensor 15 or right pressure sensor 16) is located at the center positions with respect to the magnet, an output signal of the Hall-effect sensor (left pressure sensor 15 or right pressure sensor 16) become zero level. When the magnet is moved or displaced, the output signal of the Hall-effect sensor (left pressure sensor 15 or right pressure sensor 16) changes approximately linearly between the positive maximum value and the negative maximum value. The code of the sensor signal, that is, polarity, shows the direction of the displacement of the lever handle 14, and the magnitude of the sensor signal is proportional to the amount of the displacement.
By operating the lever handle 14 forwardly and rearwardly, the lever handle 14 can be relatively easily displaced by the spring action of the spring members, and at the same time, when the lever handle 14 is released, the lever handle 14 can be quickly returned to a neutral position or a center position.
The conventional X-ray photographing apparatus is structured as described above, and it has a mechanism that both ends of the lever handle 14 are supported by the plate springs as the spring members. While the plate springs support a load in a direction of gravity, the lever handle 14 is returned to the neutral position when the operational force is zero. Also, for the detection of the operational force, there is used a method in which a position of the magnet attached to the lever handle 14 is detected by the Hall-effect sensor. Also, there can be used a method in which a strain gauge is bonded to the plate spring supporting the lever handle 14. Further, in response to the force Ft for pushing the lever handle 14, the signal of the rotational frequency Vt is received, so that the duty width of the PWM control circuit 10 is fed back and controlled.
However, in case of suddenly changing the operation, the apparatus acts unnaturally, and can not be operated well. Also, in the direct current (DC) motors (right motor 6 and left motor 5), even if the PWM control circuit 10 carries out the same duty (proportions of ON and OFF are the same) control, there is caused a phenomena that the output torque T is decreased in inversely proportional to the rotational frequency Vt. In the method that the force Ft for pushing the lever handle 14 is amplified and outputted from the motors (right motor 6 and left motor 5), even though the lever handle 14 is pushed by the same force Ft, there is caused a phenomena that the output torque T is reduced as the speed increases. Thus, it is difficult to achieve the comfortable and natural operation.
In particular, in case of driving the heavy-weight apparatus, such as the movably type X-ray photographing apparatus, the motors (right motor 6 and left motor 5) having the large torque T are adopted. Thus, when the motors (right motor 6 and left motor 5) are controlled at the amplification rate such that enough torque T can be obtained even at high speed, the motors provide torque T, which is more than required at low speed, resulting in extremely lowering the operation feeling. Also, if the amplification rate is reduced in order to improve the operation ability at the low speed, a high-speed movement of the apparatus can not be maintained without continuously applying the strong or big force to the lever handle 14, resulting in that the apparatus is not suitable for a practical use.
Accordingly, the present invention has been made in view of the foregoing, and an object of the invention is to provide a movable type X-ray photographing apparatus, which can be operated with a natural operation when an operator pushes the lever handle.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the present invention provides a movable type X-ray photographing apparatus, which comprises an operation handle attached to a moving device or base of an X-ray photographing apparatus; a plurality of pressure sensors individually disposed at right and left, and front and rear portions of the handle to be pressed in response to an operation force applied to both ends of the handle in a forward direction to thereby detect the operation force and issue signals thereof; a pair of wheels individually driven; a pair of motors disposed at axles of the wheels for driving the wheels; bridge circuits for driving including switching elements, each motor being electrically located at a center of the bridge circuit; pulse width control circuits for controlling ON-OFF duty of torques of the motors by the bridge circuits; a pair of encoders for detecting rotational speeds of the driven wheels and issuing signals of the rotational speeds; and a central processing unit (CPU) controlling the torques of the motors in accordance with the signals from the pressure sensors and the signals from the encoders to rotate the wheels for moving the X-ray photographing apparatus. The CPU controls a pulse width of the pulse width control circuit proportional to a value calculated by a formula, that is, {(a maximum value of a pulse control width)/(a maximum output torque of the motor)}xc3x97{(a maximum rotational number of the motor)/(the maximum rotational number of the motorxe2x88x92a rotational number of the motor)}xc3x97(a force for pushing the operation handle).
The X-ray photographing apparatus of the invention is structured as described above, and upon receiving the input signal F for pushing the operation handle and the input signal of the rotational frequency V of the motor, the CPU calculates the formula: {(the maximum value of the pulse control width)/(the maximum output torque of the motor)}xc3x97{(the maximum rotational number of the motor)/(the maximum rotational number of the motor xe2x88x92the rotational number V of the motor)}xc3x97(the force F for pushing the operation handle), to thereby control the pulse width W of the PWM control in the pulse width control circuit. Then, the switching element of the motor driving circuit is turned ON-OFF with the duty of the pulse width W, to thereby rotate the direct current motor. Accordingly, since the aforementioned calculation is carried out while maintaining the relationship expressed by a formula: an output torque T of the motor =(amplification factor xcex1) xc3x97(the pushing force F), the apparatus can be operated with a natural operation touch when the operator pushes the operation handle.